Looking at the photo, the height of the opening of the manifold looks bigger than the exhaust opening of the engine, I dont think this will seal properly. If I am wrong, then the dremeling I would also recomend to widen the header opening to match the engine's exhaust opening. I think most headers opening does not exactly match the exhaust opening, its usually smaller, except on rear exhaust with round ports. This is the easiest mod done with nitro engines which gives it a little more power because the air is not restricted.